The present invention is directed to a brake release system for a work vehicle having spring applied hydraulically released brakes.
Many large work vehicles are provided with spring applied hydraulically released brakes. These brakes are constantly applied by springs. The brakes are released by directing pressurized hydraulic fluid to the brakes to compress the springs. Typically these brakes cannot be released unless the engine is running and the source of pressurized hydraulic fluid, a pump, is directing pressurized hydraulic fluid to the brakes. Sometimes the engines or the hydraulic pumps on these machines break down in remote locations where they are inconvenient to repair. This is especially true in forest fire applications where moving the vehicle is time critical. However, as the brakes are in the applied mode it makes towing the vehicle difficult if not impossible. Therefore another source of pressurized hydraulic fluid needs to be applied to the brakes before towing the vehicle. Vehicle mounted manually operated hydraulic pumps have been proposed to supply a source of pressurized hydraulic fluid. In addition electrically actuated brake valves are also known.
It is an object of the present invention to provide a brake release system for spring applied hydraulically released brakes from a secondary hydraulic system.
A work vehicle is provided with a dual path hydrostatic transmission and spring applied hydraulically released brakes. The dual path hydrostatic transmission comprises left and right variable displacement pumps supplying pressurized hydraulic fluid to left and right hydraulic motors. Charge pumps for the variable displacement pumps provides a source of pressurized hydraulic fluid through a brake system hydraulic line to the spring applied hydraulically released brakes. This pressurized hydraulic fluid is selectively applied to the brakes by an electrically actuated two-position solenoid brake valve.
A controller controls the hydraulic output of the variable displacement pumps and the activation of the brakes through the brake valve. The controller receives operator inputs from an ignition switch, a brake pedal and a steering input element. The brake pedal sequentially moves through a first arc segment and then a second arc segment. As the brake pedal is moved through the first arc segment the hydraulic outputs of the variable displacement pumps are reduced and the vehicle is decelerated. As the brake pedal moves into the second arc segment the spring applied hydraulically released brakes are applied.
The vehicle is provided with a secondary hydraulic system for tilting the operator""s station for access to maintain various assemblies on the vehicle. The secondary hydraulic system, comprises a manually operated hydraulic pump and a hydraulic cylinder for tilting the operator""s station. A secondary system hydraulic line extends between the manually operated hydraulic pumps and the hydraulic cylinder. The secondary system hydraulic line is provided with a first hydraulic quick coupling and a second hydraulic quick coupling. These quick couplings are coupled to one another to form a flow path to direct pressurized hydraulic fluid from the manually operated pump to the hydraulic cylinder. When the vehicle needs to be towed the first quick coupling is decoupled from the second quick coupling and coupled to a third hydraulic quick coupling located on the brake system hydraulic line. A key is placed in the ignition to signal the controller to shift the electrically actuated brake valve, and the manually operated hydraulic pump is pumped directing pressurized hydraulic fluid from the secondary hydraulic system through the first and third hydraulic quick couplings to the spring applied hydraulically released brakes. The hydrostatic transmission is also short circuited to allow the ground engaging means to freewheel.